The administration stepped warily into the rubble of a shattered Soviet Union by hailing the outcome of Sunday`s referendum in the nation`s second most powerful republic. But it stopped short of extending full diplomatic recognition to Ukraine, which as an independent nation would rank alongside France in size and population (52 million) and conceivably could retain control over nuclear weapons within its borders.

Boris Yeltsin`s Russian republic did recognize Ukraine`s independence Monday, as did the government of Poland, the first country to do so. Prime Minister Brian Mulroney of Canada said his nation also will recognize Ukraine as an independent country and will shortly open negotiations on establishing diplomatic relations.

Bush administration officials said formal U.S. recognition is likely, perhaps within weeks, despite concerns that such a move would undermine Gorbachev`s faltering efforts to forge a union treaty on economic relations.

President Bush on Monday dispatched a special emissary, Assistant Secretary of State Thomas Niles, to Kiev to begin talks about future relations. Bush also directed Secretary of State James A. Baker III to go to the Ukrainian capital and Moscow in about two weeks.

Faced with the latest evidence of the unraveling Soviet state, the administration linked diplomatic recognition to the willingness of the Ukrainian leaders to address American concerns about human rights, economic policies, control over nuclear weapons and adherence to arms-control agreements.

These amount to criteria that also could provide a framework for subsequent decisions as other Soviet republics seek to assert their independence and be recognized by Washington. The administration is likely to feel political pressure to go ahead with recognition from Ukrainian-Americans and from the AFL-CIO, which has supported Ukraine`s democratic trade unions.

White House spokesman Marlin Fitzwater implied that the administration expects that to happen.

``The United States looks forward to the kind of normal diplomatic relations with Ukraine that one would expect to have with a democratizing country,`` he said.

Just four months ago, during a stopover in Kiev after his Moscow summit, Bush warned about what he called ``suicidal nationalism`` and voiced support for Gorbachev even as he said the U.S. would not choose sides between Moscow and the republics.

As the political breakup of the Soviet Union gained momentum in the aftermath of the collapse of the August coup, the administration has tried to walk a narrow line between supporting Gorbachev`s efforts to maintain some central authority and the determined efforts of many republics to gain independence.

Bush`s decision to move toward recognizing Ukraine`s independence marks a clear shift away from the central government. Fitzwater said Bush discussed the U.S. position over the weekend in telephone calls to Gorbachev and Yeltsin.

If the U.S. now deals directly with the leaders of the two most important Soviet republics, Russia and Ukraine, on issues from financial aid to arms control, that largely eliminates Gorbachev`s domestic role as the vital link with the West.

The administration`s decision on how to handle Ukraine is a critical one because of the republic`s importance. The breadbasket of the Soviet Union, it also is one of the four republics that house the Soviet nuclear arsenal-a fact that particularly concerns the U.S. and its Western allies. Ukraine has silos holding as many as 176 multiple-warhead strategic nuclear missiles, plus a share of the Soviet Union`s tactical nuclear arsenal. One major Western worry is conflict between Ukraine and Russia over nuclear weapons.

Leonid Kravchuk, the Ukrainian leader elected president in Sunday`s balloting, has called for the removal of all nuclear weapons stationed in Ukraine. But more recently he has opposed sending the weapons back to Russia and called for joint Ukrainian-Soviet control over them.

The U.S. wants to know what plans Kravchuk has for Ukraine to give up the nuclear weapons. The U.S. also wants a commitment from him that an independent Ukraine will assume the obligations of complying with arms-control agreements signed by the Soviet Union, in particular the new Strategic Arms Reduction Treaty (START) and an East-West treaty reducing conventional forces.

In the area of human rights, the U.S. is seeking assurances that Ukraine will protect the rights of the 12 million ethnic Russians living there and will avoid explosive disputes with Russia over borders.

Additionally, Niles, the special U.S. emissary, will discuss Ukraine`s commitment to making the transition to a free-market economy and its obligations to carry its share of the debts of the Soviet Union.

On Monday, the Bush administration also accelerated aid to the 12 republics, making immediately available $100 million in loan guarantees originally scheduled for release next year. With these credits, the republics will be able to borrow $600 million to import U.S. wheat, corn and other farm commodities.